She was born Anne-Thérèse Guérin on October 2, 1798, in the village of Étables-sur-Mer in Brittany, France. Her parents were Laurent Guérin, an officer in the French Navy under Napoleon Bonaparte, and Isabelle Guérin, née Lefèvre. Anne-Thérèse was born near the end of the French Revolution, which had torn France apart and caused a crisis within French Catholicism. Schools and churches were closed, and many Catholic priests had chosen exile over the guillotine.[1]

Laurent and Isabelle had four children, but only two — Anne-Thérèse and Marie-Jeanne — survived to adulthood. Anne-Thérèse was mostly educated at home by her mother. At the age of 10, she was allowed to take her First Communion, which was two years earlier than the custom of the time. On the day of her First Communion, she confided to the priest in Etables that she wished to enter a religious community.

When Anne-Thérèse was 15, tragedy struck the family when her father was killed by bandits as he travelled home to his family. The grief proved to be too much for her mother, who already had lost two children, and she fell into a deep and incapacitating depression. For many years, Anne-Thérèse accepted the responsibility of caring for her mother and sister, as well as the family's home and garden. At the age of 20, Anne-Thérèse asked her mother's blessing to join a religious order, but Isabelle — still unable to cope with her loss — refused. Five years later, Isabelle recognized the depth of Anne-Thérèse's devotion and permitted her to leave.[1]

Anne-Thérèse entered the young congregation of the Sisters of Providence of Ruillé-sur-Loir. She was given the religious name Sister St. Théodore. She professed first vows September 8, 1825, and perpetual vows, which at the time were optional, on September 5, 1831.

Sister St. Théodore was first sent to teach at Preuilly-sur-Claise in central France. There, she became ill, most likely with smallpox, and nearly died. The illness damaged her digestive system and, for the rest of her life, she could only eat a simple, bland diet.[2]

During her career in France, Sister St. Théodore also taught at St. Aubin parish school in Rennes and taught and visited the sick and poor in Soulaines in the Diocese of Angers. During this time, she received a medal for her teaching from the inspector for the Academy of Angers.[3]

In 1839 the Most Reverend Simon William Gabriel Bruté, the first bishop of the vast Diocese of Vincennes, Indiana, sent Célestine Guynemer de la Hailandière as a representative to their native France. Bruté was in search of a religious congregation to come to the diocese and teach, provide religious instruction, and assist the sick. With only a few priests and a great influx of Catholic immigrants of French, Irish and German descent, the diocese was in need of assistance. Bruté knew the great assistance a religious order could provide, having worked with Mother St. Elizabeth Ann Seton and her Sisters of Charity during the founding and early years of Mount Saint Mary's University in Emmitsburg, Maryland.[1]

While Hailandière was in France, Bishop Bruté died in Vincennes, and Hailandière was then consecrated bishop of the diocese. One of the first acts of the newly ordained bishop was to request the Sisters of Providence of Ruillé-sur-Loir to send a group of sisters to minister in Vincennes.

The superior general of the Sisters of Providence suggested Sister St. Théodore for the task. Although she was unsure of her own abilities to complete such a mission at first, after considerable discernment, Sister St. Théodore agreed. Later she said that it was a sentence from the Rule of the Congregation, "The Congregation being obliged to work with zeal for the sanctification of souls, the sisters will be disposed to go to whatsoever part of the world obedience calls them," that convinced her to answer the American call.

In July 1840, Sister St. Théodore and five companions (Sister Olympiade Boyer, Sister Saint Vincent Ferrer Gagé, Sister Basilide Sénéschal, Sister Mary Xavier Lerée and Sister Mary Liguori Tiercin) departed from France to sail to America. After a treacherous journey across the Atlantic Ocean, the six women traveled by steamboat and stagecoach to the dense forest of the Indiana territory.[4]

On October 22, 1840, Sister St. Théodore and her companions stepped from a carriage into the wilds Saint Mary-of-the-Woods, Indiana, a small village in Vigo County a few miles northwest of Terre Haute. For several months, they lived packed into the small frontier farmhouse of the local Thralls family along with a few postulants that had been waiting for them when they arrived. With the founding of this new order separate from that in France, Guerin became known as Mother Theodore, the superior of the Sisters of Providence of Saint Mary-of-the-Woods.[5]

Despite their humble resources, in July 1841 Guerin and the sisters opened St. Mary's Academy for Young Ladies, which later became Saint Mary-of-the-Woods College. Guerin did have doubts concerning the success of the institution. In her journals is written, "It is astonishing that this remote solitude has been chosen for a novitiate and especially for an academy. All appearances are against it."[6] For more than a decade, from 1841 to 1852, this Academy was the only Catholic boarding school for girls in Indiana.

In an attempt to help parishes establish schools for their children, Mother Théodore, from the time of her arrival at Saint Mary-of-the-Woods in 1840 to January 1849, established parish schools at Jasper, St. Peter's, Vincennes, Madison, Fort Wayne and Terre Haute, all in Indiana, and at St. Francisville in Illinois. In 1853, she opened establishments in Evansville, Indiana and North Madison, Indiana; in 1854, at Lanesville, Indiana; and in 1855 at Columbus, Indiana, south of Indianapolis.

Additionally, with Bishop de Saint-Palais, she established two orphanages in Vincennes.

Guerin proved to be a skilled businesswoman and leader as well as a beloved general superior. By the time of Mother Théodore's death in 1856, the Sisters of Providence congregation had grown from six sisters and four postulants to 67 professed members, nine novices and seven postulants.

After a period of sickness, Guerin died at age 57 on May 14, 1856. The Catholic Telegraph and Advocate in Cincinnati, published the following notice about Mother Théodore's death.

Died - At Saint Mary's-of-the-Woods (sic), in the 58th year of her age, Wednesday, 14th inst., Sister St. Théodore, Superior General of the Sisters of Providence in Indiana.

This woman, distinguished by her eminent virtues, governed the community of which she was the superior from its commencement, to the time of her death, a period of nearly sixteen years. Being a perfect religious herself, and endowed with mental qualities of a high order, she was peculiarly fitted to fill the duties which Providence assigned her.

Not only her Sisters are bereaved by her death, but all those who knew her excellence and the amount of good she did, join in lamenting that she should have been removed from the sphere of her usefulness. To judge from the celestial expression of her countenance as she lay in death, there is every reason to believe that she has already taken her abode among the Saints in Heaven, enjoying the munificence of God, who rewards His servants 'according to their works.'

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